Apparatus and methods for treating vascular conditions, and more specifically, materials for use in treating such conditions, are described.
Stent-graft assemblies may be used to treat a number of medical conditions. One common use of stent-graft assemblies relates to the treatment of an aneurysm, which is an abnormal widening or ballooning of a portion of an artery that may be caused by a weakness in the blood vessel wall. In many cases, the internal bleeding is so massive that a patient can die within minutes of an aneurysm rupture. For example, in the case of aortic aneurysms, the survival rate after a rupture may be as low as 20%.
In an endovascular treatment of a blood vessel using a stent-graft, the stent-graft is positioned in the blood vessel across the aneurysm, e.g., using catheter-based placement techniques. The stent-graft treats the aneurysm by sealing the wall of the blood vessel with a generally impermeable graft material. Thus, the aneurysm is sealed off and blood flow is kept within the primary passageway of the blood vessel. Although stent-grafts are frequently used for treating aneurysms, other medical treatments also use stent-grafts and still other uses are possible, such as uses for treating aortic dissections, stenosed arteries or other conditions.
Various types of stent-grafts are constructed with a stent disposed inside graft material, outside of graft material, or between inner and outer layers of graft material. The stents commonly are coupled to the one or more layers of graft material. For example, one technique for securing graft material to a stent involves securing one or more graft layers to the struts of the stent.
Another technique that is used for securing graft layers to a stent generally involves encapsulating the stent or a portion thereof with an inner and an outer layer of graft material. In this type of stent-graft, the two layers of graft material are adhered to each other through open areas in the stent structure. Some additional bonding may also occur between each graft layer and the stent structure itself, for example, the inner and outer graft layers may be adhered by heating or using adhesives.
In constructing stent-grafts, it may be difficult to furnish a reliable prosthesis having a relatively small diameter delivery profile, such that the prosthesis may be delivered into smaller vessels. Notably, the inventors have determined that the fabric portion of a stent-graft can contribute significantly to the overall delivery profile of a stent-graft. For example, graft material, depending on its thickness, may contribute between about 50-80% of the overall volume of a stent-graft's profile in a delivery configuration. Thus, such relatively large prostheses may not be capable of delivery into smaller vessels. However, the fabric used in stent-grafts for endovascular graft repair must maintain important and unique requirements, including sufficient tensile strength, permeability, biocompatibility, and overall bulk, and such properties should not be compromised in order to achieve the desired smaller profile.